We use the embedding tensor method to construct the most general maximal gauged/massive supergravity in d=9 dimensions and to determine its extended field content. Only the 8 independent deformation parameters (embedding tensor components, mass parameters etc.) identified by Bergshoeff et al. (an SL(2,R) triplet, two doublets and a singlet can be consistently introduced in the theory, but their simultaneous use is subject to a number of quadratic constraints. These constraints have to be kept

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... d enforced because they cannot be used to solve some deformation parameters in terms of the rest. The deformation parameters are associated to the possible 8-forms of the theory, and the constraints are associated to the 9-forms, all of them transforming in the conjugate representations. We also give the field strengths and the gauge and supersymmetry transformations for the electric fields in the most general case. We compare these results with the predictions of the E11 approach, finding that the latter predicts one additional doublet of 9-forms, analogously to what happens in N=2, d=4,5,6 theories.